1. Technical Field
The present invention relates to an electromagnetic-wave transmitting cover.
2. Related Art
A. C. C. (abbreviation of Adaptive Cruise Control) is a technique that measures an inter-vehicle distance or a relative speed between one's own vehicle and a preceding vehicle with a sensor mounted on the front side of the vehicle, and controls a throttle and a brake on the basis of the obtained information to accelerate or decelerate its own vehicle so as to control the inter-vehicle distance. In recent years, this system has attracted attention as one of core competencies of an intelligent transport system (abbreviation: ITS) oriented toward moderation of traffic congestion and accident reduction.
As a sensor used in the A. C. C., in general, a laser radar or a millimeter-wave radar is used. For example, the millimeter-wave radar transmits a millimeter wave having frequencies of 30 GHz to 300 GHz and wavelengths of 1 to 10 mm and receives the millimeter-wave hit and reflected by an object to measure an inter-vehicle distance and a relative speed between one's own vehicle and a preceding vehicle on the basis of a difference between the transmitted wave and the received wave.
A radio-wave radar for vehicle device which transmits/receives a laser or a millimeter wave is generally disposed on the rear side of a front grille (unless otherwise stated, longitudinal directions, width directions, and the like correspond to directions defined with reference to a vehicle hereinafter). The front grille has an uneven thickness, and is made of metal or has a metal-plated layer formed on a surface thereof. Thus, the front grille interferes with a pathway of a radio wave (for example, a millimeter wave). For this reason, a technique that forms a window portion in a part of the front grille corresponding to the front side of the vehicle radio-wave radar device and fits a resin electromagnetic-wave transmitting cover in the window portion.
The electromagnetic-wave transmitting cover is located on a vehicle front surface and has a design layer to express various designs formed thereon. The design layer is a relatively thin layer that is formed by metal deposition, film transferring, or the like. For this reason, the front surface and the rear surface of the design layer need to be covered with reinforcing resin layers, respectively (for example, Japanese Patent No. 4888732).
Japanese Patent No. 4888732 describes a electromagnetic-wave transmitting cover including a front-side member having a transparent layer and a design layer, a rear-side member laminated on a rear-surface side of the front-side member, and a coupling layer laminated on an edge portion of at least one of the front-side member and the rear-side member and fixed to both the members, wherein both the members are formed as separated members and spaced apart from each other by 0.01 mm to 0.4 mm in longitudinal direction.
In the electromagnetic-wave transmitting cover described in Japanese Patent No. 4888732, a gap between the front-side member and the rear-side member is adjusted to reduce a loss caused by the gap (more specifically, an atmospheric air layer filled in the gap).